Combustion apparatus and controlled draft inducer



Oct. 25, 1966 R. M. ENGLISH COMBUSTION APPARATUS AND CONTROLLED DRAFT INDUCER Filed Feb. 12, 1965 I ROBERT M. ENGUSH wM gw ATTORNEYS United States Patent 3,280,774 COMBUSTION APPARATUS AND CONTROLLED DRAFT INDUCER Robert M. English, 224 Altondale Ave., Charlotte, N.C. Filed Feb. 12, 1965, Ser. No. 432,093 5 Claims. (Cl. 110-162) My invention pertains to combustion apparatus and more particularly to such combustion apparatus including a controlled draft inducer which provides an induced draft for the combustion apparatus which is controlled in correlation to the combustion process to promote more eflicient use of the fuel being burned therein.

As generally recognized, the greatest efficiency of burning in a combustion apparatus is reached when combustion occurs with chemically correct quantities of air and fuel, and this type of burning is termed stoichiometric. In actual practice, stoichiometric burning cannot be achieved, and a predetermined slight excess of air above the stoichiometric quantity is required in order to avoid sooty combustion. For best results, the amount of air delivered to a combustion chamber should be accurately controlled and correlated to the rate at which the fuel is being delivered thereto to assure that the fuel is completely burned and in a manner whereby undesirable combustion by-products, such as excessive smoke, soot and the like are not formed.

Unfortunately, conventional combustion apparatus, such as furnaces, boilers and the like, do not approach stoichiometric burning and are generally relatively inefficient. Such conventional combustion apparatus may generally be classified as two types, the first type being those which rely upon natural draft, and the second type being those which have a draft inducer associated therewith. Those conventional combustion apparatus relying upon natural draft, i.e., the natural tendency of hot air and gases to rise, for the removal of combustion products from the combustion chamber and the drawing of fresh air into the combustion chamber by the partial vacuum created upon the removal of combustion products therefrom, have the combustion chamber connected directly to a flue or chimney.

In such conventional combustion apparatus, there are generally three types of means for attempting to control the draft through the combustion chamber. The first type of such draft control means comprises a valve means at the air inlet to the combustion chamber which may be set to vary the open area of the air inlet in an attempt to control the amount of air which may be drawn therethrough into the combustion chamber. The second type of draft control means for such conventional combustion apparatus comprises damper means positioned within the flue or chimney and which may be set to control the amount of combustion products which may rise through the flue or chimney and thus control the draft through the combustion chamber. The third type of such draft control means comprises a combination of the air inlet valve means and the flue or chimney damper means.

All of these types of draft control means for use with natural draft combustion apparatus are very inaccurate and extreme difficulty is encountered in attempting to set such control means to properly correlate the draft through the combustion chamber to the rate at which fuel is being consumed in the combustion chamber. This difficulty in properly setting such conventional draft control means frequently results in an improper draft which, in turn, results in improper combustion and the formation of undesirable combustion-by-products, such as excessive smoke, excessive soot, and noxious odors or gases and the like. In addition, due to the relatively open condition of the flue or chimney and its direct connection to the combustion chamber, considerable heat is lost up the flue or chimney from the combustion chamber and in this respect is wasted. Further, quite frequently air currents outside the flue or chimney offset the natural tendency of the combustion products to rise through the fiue or chimney and force the same downwardly back into the combustion chamber which results in a so-called down-draft which materially interferes with the combustion process within the combustion chamber and quite frequently completely terminates combustion.

Recognizing the deficiencies of such conventional draft control means and reliance upon natural draft in the above-discussed type of conventional combustion apparatus, several attempts have been made to provide combustion apparatus with draft inducers to induce a draft in an attempt to more closely approach stoichiometric buming. Such draft inducers classically operate on an ejector principle, with a fan being used to direct a relatively small quantity of fresh air up the flue or chimney to create a vacuum effect therein to draw combustion products from the combustion chamber and to carry such combustion products up the flue or chimney. Upon such drawing of combustion products from the combustion chamber, fresh air is drawn into the combustion chamber in a like amount to be combined with the fuel therein for combustion.

At most, these conventional draft inducers have been only moderately successful. For example, while these draft inducers normally operate simultaneously with the combustion apparatus, the conventional combustion apparatus is, in fact, operated independently of the draft inducer. Accordingly, the draft inducers must provide for natural draft, in case the draft inducers break down or are rendered inoperative for any reason during operation of the combustion apparatus, as is required by most building codes. Therefore, while reducing the problem of down-draft to some extent, such draft inducers do not eliminate this problem, which continues to frequently manifest itself. Additionally, the direct connection between the combustion chamber and the flue or chimney required for even partial natural draft operation permits considerable heat to be lost up the flue or chimney and accordingly wasted. Further, and probably most importantly, the draft through the combustion chamber is not positively controlled since a vacuum effect is relied upon to draw the combustion products from and fresh air into the combustion chamber, and the resultant flow created by this vacuum effect is not consistent. Inconsistencies result from, for example, fluid currents set up within the flue or chimney which interfere with the creation of the vacuum effect and varying effects due to atmospheric conditions surrounding the draft inducer inlet and flue or chimney outlet.

The combustion apparatus and controlled draft inducer of my invention avoids these deficiencies and difficulties of conventional combustion apparatus and draft inducers by providing a positive draft limiting the flow of combustion gases from and air into the combustion chamber to a rate correlated to the fuel supply rate, assuring a positive draft at the desired rate of flow before combustion begins, and presenting sufficient resistance to the vagrancies of natural draft effects to preclude termination of combustion or waste of heat by such effects.

Accordingly, it is an object of this invention to provide improved combustion apparatus which obviates the aforementioned deficiencies of conventional combustion apparatus with or without draft inducers by including a I draft inducer providing an induced flow of combustion products which is correlated to the rate of fuel use in the combustion process to approach stoichiometric burning.

A more specific object of this invention is to provide an improved draft inducer of the character described wherein the flow of combustion products through the combustion apparatus is positively controlled in correlation to the rate at which fuel is being delivered to the combustion chamber.

Another object of this invention is to provide an improved draft inducer for combustion apparatus wherein operation of the combustion apparatus is controlled in response to operation of the draft inducer thereby obviating the requirement for natural draft and its attendant disadvantages.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in which FIGURE 1 is a fragmentary, partially schematic, perspective view of an illustrative type of a combustion apparatus incorporating a draft inducer embodying the features of the present invention;

FIGURE 2 is an enlarged exploded perspective View of the draft inducer shown in FIGURE 1;

FIGURE 3 is an enlarged fragmentary sectional view, taken substantially along line 3-3 in FIGURE 1; and

FIGURE 4 is an elevational view of selected orifice plates of a set of orifice plates-forming a part of the draft inducer of this invention.

As illustrated in FIGURE 1, the controlled draft inducer of my invention, indicated generally at 10, is adapted for use in combination with a combustion apparatus, indicated generally at 11. As here illustrated, the combustion apparatus 11 is an oil-fired hot air furnace, such as'might be used for residential heating. However, the draft inducer apparatus is useful not only with the particular type of combustion apparatus chosen for illustration in the drawing, but is useful generally with a wide range of types of combustion apparatus, including but not limited to hot air furnaces fired with any fuel, boilers, water heaters and other fluid heat exchangers.

In the specific combustion apparatus 11 hown, a controllable means is provided for supplying fuel, which may be an oil burner 12. As generally well known, an oil burner is adjusted, at the time of installation, to deliver fuel at a particular predetermined rate, and usually expressed in terms of gallons per hour, correlated to the heat required for the particular space to be heated. Thereafter, in use the burner is controllably operated to be either on or off, in order to meet varying heat rate demands, rather than controllably operated to vary the rate of supply of fuel from the predetermined rate. Fuel supplied from the oil burner 12 is introduced into a combustion chamber 13, and means, such as passages through the housing of the burner 12, are provided for admitting air into the combustion chamber 13 for combustion therein with the fuel supplied by the oil burner 12. The combustion chamber 13 is provided with a combustion products outlet 14, through which the gaseous products of combustion are removed from the combustion chamber 13. The combustion products leaving the combustion chamber 13 through the outlet 14 are conveyed through a flue 15, to be dispersed in the ambient atmosphere.

In conventional installations of an oil burning hot air furnace, such as the combustion apparatus 11 here used as an illustration for the application of this invention, a control system including a room thermostat 17, located in the area to be heated, is employed to control the operation of the combustion apparatus 11. Other elements of the control system, as conventionally well known, include a stack switch 20, an oil control valve 21, an oil burner motor 22, and an ignition transformer 23. The conventional steps in the control operation for such a combustion apparatus 11 are for the thermostat 17 to indicate a cold condition in the room and actuate the stack switch 20 to open the oil control valve 21 and permit fuel to flow to the burner, to initiate operation of the burner motor 22 and introduce fuel into the combustion chamber 13, and to energize the ignition transformer 23 to light off a flame within the combustion chamber 13. When the room thermostat 17 is satisfied, the burner motor 22 is stopped and the fuel oil valve 21 i closed, terminating combustion.

As shown in FIGURES 1 through 3 of the drawings, the controlled draft inducer of this invention comprises a fan means including a scroll housing 24, a squirrel cage fan rotor 25 supported for rotation within the scroll housing 24, and a fan motor 26 connected to the rotor 25 to drive the rotor and cause a flow of gases through the scroll housing 24 and thus through the fan means. The scroll housing 24 has an inlet, as defined by a laterally extending flange 27, and an outlet 28. As best illustrated in FIGURE 3, the inlet flange 27 is adapted to be connectable to the combustion products outlet 14 of the combustion apparatus 11, which is preferably accomplished by the use of a double flanged adapter 30 secured to a laterally projecting flange 31 of the combustion products outlet 14 and to the flange 27 of the fan housing 24. The fan outlet 28 i adapted to be connected to the flue 15. When so connected to the combustion apparatus 11, the fan means, on operation of the fan motor 26, draws combustion products from the combustion chamber 13 through the combustion products outlet 14 and discharges the combustion products through the flue 15, irrespective of natural draft effects, to be dispersed in the atmosphere.

The forced fiow of combustion products through the flue 15, during operation of the fan means, is adequate to overcome the vagrancies of natural draft effects, and particularly to overcome any down draft which would otherwise force combustion products back into the combustion chamber 13. Further, relatively small free areas between the blades of the fan means rotor 25 present a sufliciently high flow resistance, when the rotor is stationary and not driven by the fan motor 26, to prevent excessive flow of combustion products from the chamber 13 under the effects of natural draft once combustion is terminated by the control system, retaining the hot combustion products so as to obtain the greatest possible extraction of heat from the products and improve economy of operation.

In order to control the flow of combustion products from the combustion chamber 13, and accordingly control the admission of air into the combustion chamber 13, this invention provides a series or set of orifice plates as illustrated in part in FIGURE 4. An individual orifice plate 32, as best shown in FIGURES 2 and 3, is disposed at the fan means inlet, being preferably mounted within the inlet flange 27 of the fan housing 24 and maintained in that position by the adapter 30, as illustrated in FIG- URE 3. The orifice plate 32 mounted at the inlet of the fan means to control the flow of combustion products is one of the series or set. As shown in FIGURE 4, the full series or set includes two sub-series or sub-sets, exemplified, for example, by orifice plates 32a and 32d. The first sub-series includes, among others, plates 32a, 32b and 32c, each having a central opening of a first predetermined size and at least one additional smaller opening around the periphery of the plate. The second sub-series, includes among others, plates 32d, 32c and 32f, each having a central opening of a second, and larger, predetermined size and a varying number of smaller peripheral openings.

As will be understood from a knowldege of fluid mechanics, an orifice plate such as the plate 32 serves a flow limiting function in that fluid flow through the orifice, with all other factors being constant, is determined by the total open area of the orifice. With an orifice plate having a central opening and a plurality of smaller peripheral openings, the total open area of the plate may be determined by adding the areas of the central opening and the smaller peripheral openings. In the series of orifice plates used with the apparatus of this invention, predetermined discrete steps of variation in flow limiting are obtained by varying the total open area of successive plates within the series in a predetermined degree, by providing more or less of the peripheral smaller openings.

The progressively larger open areas provided in the series of plates are related to the operating characteristics of the fan means so as to limit the flow of combustion products through the fan means to predetermined rates and, inasmuch as the flow of combustion air into the combustion chamber is dependent upon the flow of combustion products from the combustion chamber, limit the flow of air into the combustion chamber to similarly predetermined rates.

The predetermined rates of air flow, and the open areas of the plates determining those rates, are determined from a mathematical and chemical analysis of theoretical stoichio'metric combustion in a typical combustion apparatus for predetermined varying rates of fuel consumption, to provide theoretically correct air for the combustion process. As supplied to a user, the series is keyed to these predetermined varying rates of fuel supply, which in the instance of an oil fired apparatus are expressed in terms of gallons per hour. That is, a table is provided correlating the plates in the series to the gallons per hour consumed by a combustion apparatus so that a plate Providing the theoretically correct rate of air flow for the particular rate of fuel flow may be readily selected.

When a combustion apparatus 11 is to be installed in a use location, the heat loss generally determines the rate of fuel delivery to the combustion chamber 13, and the fuel supply means 12 is adjusted, at the time of installation, to the required predetermined rate of fuel flow. The draft inducer of this invention is initially installed with an orifice plate 32 selected from the applicable table as having an open area theoretically correlated to the predetermined rate of fuel supply for which the fuel supply means 12 of that apparatus is adjusted. Then, the combustion apparatus 11 and draft inducer apparatus are placed in operation, and suitable tests, as for smoke and other combustion by-products, are conducted in order to determine if the proper controlled draft is being induced in the combustion apparatus. Should the tests reveal that the theoretically correct flow of air is improper for the particular situation, as either providing excess air or insuflicient air for proper combustion, the originally installed orifice plate is replaced with another plate in the series, to provide an open area properly correlated to the actual operating characteristics of the combustion -apparatus 11.

In order to assure that combustion may not be initiated in the combustion chamber 13 absent the proper and established draft and air flow, my invention provides means responsive to the operation of the fan means for controlling the operation of the fuel supply means 12. Preferably, this means is a centrifugal switch 33, illustrated schematically in FIGURE 1, and housed within a switch housing 34 mounted on the fan motor 26. The centrifugal switch 33 is driven from the fan motor shaft, and operates to close an electrical circuit when the fan motor speed reaches a level adequate to provide the required induced draft, by driving the fan rotor 25. As illustrated schematically in FIGURE 1, the centrifugal switch and fan motor are so wired into the control system for combustion apparatus 11 that the initial operation, on the room thermostat 17 calling for heating, is the actuation of the fan motor 26. When the fan motor 26 and rotor 25 reach operating speed and draft and air flow are established, the centrifugal switch 33 closes and actuates the fuel supply means, including the burner motor 22, the oil cut-off valve 21 and the ignition transformer 23, to initiate combustion in the combustion chamber 13. When the room thermostat 17 is satisfied, the circuit to the draft inducer fan motor 26 is broken and, as that motor slows down, the centrifugal switch 33 opens to terminate the supply of fuel to the combustion chamber 13.

In operation, with the required orifice plate installed, as combustion takes place within the combustion chamber 13, the flow of air into that chamber i limited, by the orifice plate 32, to a rate correlated to the rate of fuel supplied by the fuel supply means 12, in order to assure proper combustion, approximating stoichiometric combustion as closely as practicable. On termination of combustion, under the control of the room thermostat 17, the flow resistance presented by the fan rotor 25 and orifice plate 32 is suflicient to prevent natural draft losses of hot combustion products gases from the combustion chamber 13 up the flue 15 and block down draft effects. This retention of hot gases in the combustion chamber provides a more economical operation of the combustion apparatus 11 here illustrated, as obtaining more extended time for transfer of heat from those hot products before they are exhausted up the flue by natural draft.

It is therefore believed apparent that the present invention provides improved combustion apparatus which more closely approaches stoichiometric burning than conventional combustion apparatus by having a controlled draft induced therein by an improved draft inducer which is controlled in correlation to the rate at which fuel is being delivered thereto. In addition, the present invention provides improved combustion apparatus which is controlled in such a manner that combustion may only occur when a proper controlled draft is induced therein.

In the drawings and specification there have been set forth preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

I claim:

1. In a combustion apparatus having a combustion chamber, means for supplying fuel to the chamber at a predetermined rate of flow preselected for correlation with with heat output required from the apparatus, means for supplying air to the chamber for combustion therein with the fuel, an outlet from the chamber for combustion products, and a flue for conveying combustion products to be dispersed in the atmosphere, the combination therewith of means for controlling the supply of air to the combustion chamber to effect combustion and the avoidance of undesirable combustion by-products and compr1s1ng:

fan means having an inlet connected to the combustion products outlet and an outlet connected to the flue for positively drawing combustion products from the chamber and directing the same up the flue and for drawing air into the chamber through said air supply means, and

means for limiting the flow of combustion products from the chamber and thus the flow of air drawn thereinto by said fan means to a predetermined rate of fl-ow preselected for correlation with the rate of fuel flow,

said means for limiting flow comprising a set of orifice plates, said plates of said set having various predetermined open areas, each plate having the open area thereof correlated to a predetermined rate of combustion products flow and being adapted to be individually selectively interposed between said fan means inlet and the combustion products outlet, so that correlation of the flow of air and fuel is obtained.

2. The combination as claimed in claim 1 further comprising:

means responsive to operation of said fan means and operatively connected to the fuel supplying means for controlling the operatiton of the fuel supplying means to upply fuel for combustion only during operation of said fan means.

3. For use with a combustion apparatus having a combustion chamber means for supplying fuel to the chamber at a predetermined rate of flow preselected for correlation with heat output required from the apparatus, means for supplying air to the chamber for combustion therein with the fuel, an outlet from the chamber for combustion products, and a flue for conveying combustion products to be dispersed in the atmosphere, means for controlling the supply of air to the combustion chamber to effect combustion and the avoidance of undesirable combustion by-produ-cts and comprising:

fan means having an inlet adapted to be connectable to the combustion products outlet and an outlet adapted to be connectable to the flue for positively drawing combustion products from the chamber and directing the same up the flue and for drawing air into the chamber through said air supply means, and means for limiting the flow of combustion products from the chamber and thus the flow of air drawn thereinto by said fan means to a predetermined rate of flow preselected for correlatiton with the rate of fuel flow, said means for limiting flow comprising a set of orifice plates, said plates of said set having various predetermined open areas, each plate having the open area thereof correlated to a predetermined rate of combustion products flow and being adapted to be individually selectively interposed between said fan means inletand the combustion products outlet, so that correlation of the flows of air and fuel supplied to the combustion chamber is obtained. 4. An apparatus as claimed in claim 3 further comprising:

means responsive to operation of said fan means and operatively connectable to the fuel supplying means for controlling the operation of the fuel supplying means to supply fuel for combustion only during operation of said fan means.

5. An apparatus as claimed in claim 3 in which said set of plates comprises:

a first series of orifice plates each having a central opening of a first predetermined size, and

a second series of orifice plates each having a central opening of a second larger predetermined size,

each of said series including orifice plates having varying numbers of additional smaller openings to provide progressively increasing areas.

References Cited by the Examiner UNITED STATES PATENTS 1,300,335 4/1919 Bohan 162 1,648,950 11/1927 Knaggs l10162 1,871,487 8/1932 Zu-cher 110147 1,892,188 12/1932 Goodridge 110162 X 2,088,299 7/1937 Macrae 15842.2 2,259,299 10/1941 Dewey 15s- 42.2 X

2,617,371 11/1952 Resek et al 110l62 2,684,647 7/1954 Bither 110163 KENNETH W. SPRAGUE, Primary Examiner. 

1. IN A COMBUSTION APPARATUS HAVING A COMBUSTION CHAMBER, MEANS FOR SUPPLYING FUEL TO THE CHAMBER AT A PREDETERMINED RATE OF FLOW PRESELECTED FOR CORRELATION WITH WITH HEAT OUTPUT REQUIRED FROM THE APPARATUS, MEANS FOR SUPPLYING AIR TO THE CHAMBER FOR COMBUSTION THEREIN WITH THE FUEL, AN OUTLET FROM THE CHAMBER FOR COMBUSTION PRODUCTS, AND A FLUE FOR CONVEYING COMBUSTION PRODUCTS TO BE DISPERSED IN THE ATMOSPHERE, THE COMBINATION THEREWITH OF MEANS FOR CONTROLLING THE SUPPLY OF AIR TO THE COMBUSTION CHAMBER TO EFFECT COMBUSTION AND THE AVOIDANCE OF UNDERSIRABLE COMBUSTION BY-PRODUCTS AND COMPRISING: FAN MEANS HAVING AN INLET CONNECTION TO THE COMBUSTION PRODUCTS OUTLET AND AN OUTLET CONNECTED TO THE FLUE FOR POSITIVELY DRAWING COMBUSTION PRODUCTRS FROM THE CHAMBER AND DIRECTING THE SAME UP THE FLUE AND FOR DRAWING AIR INTO THE CHAMBER THROUGH SAID AIR SUPPLY MEANS, AND MEANS FOR LIMITING THE FLOW OF COMBUSTION PRODUCTS FROM THE CHAMBER AND THUS THE FLOW OF AIR DRAWN THEREINTO BY SAID FAN MEANS TO A PREDETERMINED RATE OF FLOW PRESELECTED FOR CORRELATION WITH THE RATE OF FUEL FLOW, SAID MEANS FOR LINITING FLOW COMPRISING A SET OF ORIFICE PLATES, SAID PLATES OF SAID SET HAVING VARIOUS PREDETERMINED OPEN AREAS, EACH PLATE HAVING THE OPEN AREA THEREOF CORRELATED TO A PREDETERMINED RATE OF COMBUSTION PRODUCTS FLOW AND BEING ADAPTED TO BE INDIVIDUALLY SELECTIVELY INTERPOSED BETWEEN SAID FAN MEANS INLET AND THE COMBUSTION PRODUCTS OUTLET, SO THAT CORRELATION OF THE FLOW OF AIR AND FUEL IS OBTAINED. 